Selecting biological control agents

Experimental confirmation of host range

Predicting indirect non-target effects of agents

What we don't know

Much of the recent research into non-target effects has concentrated on
two-species interactions compared with the more subtle indirect interactions
such as competition and apparent competition (Messing et al. 2006). In part this
is because despite mounting information about community dynamics and how to
study them, the inherent complexity and uncertainty of interactions within
receiving communities makes rational decision-making about non-target effects
difficult (van Lenteren et al. 2006). Babendreier et al. (2006) have reviewed
the various international attempts at developing regulations for biological
control, and detail the information requirements of the OECD on environmental
risk assessment of biological control agents. Although information on
competition and other indirect effects are now required by regulators like the
OECD, it unclear how this will be achieved (Babendreier et al. 2006. With
relatively few exceptions, studies reporting non-target effects provide
information about effects at the level of the individual, such as percentage
damage and percentage mortality. Messing et al. (2006) and others propose that
evaluation of indirect effects should concentrate on population and community
level effects rather than effects on individuals, and need to be field-based and
long-term, to isolate temporal and spatial variation. Lockwood (2000) also
considered that the conservation of 'species' as a basis for non-target impact
assessment lacked depth. He made the case that a population is not a collection
of individuals but the energy and nutrient flows that manifest through the
individual. For this reason, in assessing impacts the emphasis should be on
population and community processes, such as reproduction, competition,
consumption, not on population size. Babendreier et al. (2005) suggested that we
need to develop better a priori definitions of what a significant non-target
effect is, and we should aspire to baseline studies before release. Such
aspirations are difficult in the research-funding environment that we work in
New Zealand, but this important suggestion should at least focus applicant's
minds on potential issues.

How important are these indirect non-target impacts to ecosystem function?
The number of deliberate introductions of exotic organisms for the purpose of
biological control is small compared with the powerful influence of invasions
caused by the accidental introduction of exotic organisms or for the deliberate
introduction for other purposes (van Driesche and Hoddle 1997). In terms of
relative risk, the role of modern biological control of pests and weeds in
environmental change in New Zealand is therefore likely to be small. In a large
survey of database information Lynch and Thomas (2000) found that only 1.5% of
the 5000 projects they reviewed recorded adverse effects, but they acknowledged
that this information was not well represented in the data. Of that 1.5%, only
10% appeared to have effects at the population level. For weed control projects
in New Zealand the adverse effects are likely to be less frequent than this
(Fowler et al. 2003).

There is debate about how prevalent significant adverse non-target effects
are, but there is no debate that these sometimes occur. Louda et al. (2003)
reviewed the known examples of adverse effects and provide views on how cases
like these might be avoided in future. Simberloff and Stiling (1996)
recommended care in the use of biological control because even if we could
predict events such as extinction of populations, it is not obvious how to
assign value. Beyond the fact that we cannot predict ripples in communities and
ecosystems (let alone species) how much is the very existence of these entities
worth? The uncertainty is made more acute by the irreversible nature of
biological control, and ability of agents to spread. They argued that while
biological control can be justified by the high threat of invasives in native
communities this does not abrogate the responsibility of biological control
practitioners to take care, a recommendation that seems entirely fair.

Hoddle (2004) stated that the published literature suggests that direct
attacks on non-target organisms by introduced control agents can be minimised by
selecting agents that are both host and habitat specific. Hawkins et al. (1999,
cited in Hoddle 2004) suggest that the trophic relationships of successful
biological control projects are less reticulate than those in food webs of
natural systems. Less successful projects have more impact on food webs because
the agent becomes permanently abundant. The best protection against subtle
non-target effects is to maximise the host specificity and efficacy of agents
(van Lenteren et al. 2006 and others).

Biological control practitioners who wish to introduce a control agent to New
Zealand are required to assess the potential for indirect non-target impacts
when it is clear that a useful framework is only just in existence.
Babendreier et al. (2006) point out that the OECD framework now requires information on the
indirect effects of prospective control agents, but how this can be achieved is
unclear.

Messing et al. (2006) concluded that practitioners and regulators have a
daunting task, as frameworks to guide prediction are rudimentary, and yet
concrete and responsible decisions need to be made. They also stressed that it
is essential that regulators do not extrapolate from observations of feeding or
parasitism in lab or field to population effects. The EPA must operate
within the limitations of our understanding of community dynamics in New Zealand
ecosystems. In the face of this complexity, applicants will be asked to provide
all available information, common sense interpretation of that information, and
an appropriate risk assessment based on that interpretation. The following tools
have been used in the interpretation of community interactions, and the examples
may assist in future risk assessments.